The present invention generally relates to a tuning fork resonator and, more particularly, to a support structure for an electrically driven tuning fork of the tuning fork resonator.
A tuning fork resonator is well known as comprising an electrically driven tuning fork including a pair of opposed fork tines connected at one end to each other by means of a common junction portion, and a support base for supporting the tuning fork in position spaced therefrom. A tuning fork resonator is commonly used as a highly selective filter for electrical signals or in conjunction with a feedback amplifier to provide a very stable oscillator.
For the purpose the discussion of the present invention, the prior art tuning fork resonator which appears to be closest to the present invention will now be described with reference to FIG. 1 of the accompanying drawings which illustrates the prior art tuning fork resonator in a schematic perspective view.
Referring now to FIG. 1, the prior art tuning fork resonator comprises a substantially U-shaped tuning fork 10 of metallic material including a pair of spaced opposed tines 11 and 12 and a common junction portion 13 integrally connected at its opposed ends with respective ends of the tines 11 and 12, the space between the opposed tines 11 and 12 forming a substantially U-shaped groove 14. This tuning fork resonator further comprises a support structure including a support base 15 of electrically insulating material and a pair of spaced support rods 16 and 17 rigidly mounted on and upwardly extending from one surface of the support base 15, the respective free ends of said support rods 16 and 17 cooperating with each other to support a portion of the tuning fork 10 intermediate the nodes of fundamental harmonic oscillation thereof, that is, a portion intermediate of the length of the common junction portion 13. The support base 15 carries a pair of electrode terminal pins 18 and 19 each having the opposite ends thereof situated on respective sides of the support base 15, a substantially intermediate portion thereof extending completely through the thickness of the support base 15. The ends of the respective terminal pins 18 and 19 adjacent the tuning fork 10 are electrically connected by means of lead wires 20 and 21 respectively to piezoelectric elements (only one of which is shown by 22) each being applied to an outer surface of the corresponding tine 11 or 12 which is remote from the other tine 12 or 11.
Where the tuning fork resonator of the construction described above and shown in FIG. 1 is to be used as an oscillator, one of the terminal pins, for example, the terminal pin 18, is electrically connected to the other terminal pin 19 through a feedback amplifier (not shown) so that an electric signal indicative of the frequency of intrinsic vibration of the tuning fork 10 can be, after having been supplied from the piezoelectric element, connected to the terminal pin 18 through the lead wire 20, to the feedback amplifier and then amplified by said feedback amplifier, supplied back to the piezoelectric element 22 to keep the tuning fork 10 vibrating at the intrinsic frequency.
The support structure employed in the prior art tuning fork resonator shown in FIG. 1 may be referred to as a two-point support system and, because of the two-point support for the tuning fork 10, the tuning fork resonator as a whole does not have sufficient resistance to shock and vibration. By way of example, once a shock or vibration is applied, either directly or indirectly, to one or both of the tuning fork 10 and the support base 15, the resonance frequency tends to vary and/or the tuning fork 10 tends to be shortcircuited with one of the terminal pins 18 and 19 or lead wires 20 and 21.
Furthermore, with the support structure shown in FIG. 1, because of the employment of the lead wires 20 and 21, the manufacture of the tuning fork resonator is complicated in that soldering at four points is required.
On the other hand, in order to avoid the above disadvantages, the tuning fork 10 might be placed directly on the support base 15. This possibility, however, has the drawback that, since the area of contact of the tuning fork 10 with the support base 15 becomes relatively large, the Q of the tuning fork resonator tends to be reduced.